Question: Suppose the diameter of a circle is ${12}$. What is its area?
Solution: ${d = 12}$ ${K = 36\pi}$ First, find the radius: $r = d/2 = {12}/2 = {6}$ Now find the area: $K = \pi r^2$, so $K = \pi \cdot {6}^2 = {36\pi}$.